In implementing computer networks, it is sometimes desirable to control a server from a client. Several products exist that permit a user to display the desktop of a remote server on a client display and control the remote server as if it were at hand. A drawback of these products is that the client must be a fully functional computer. This is undesirable from a cost and maintenance point of view.
Implementing such control of a server from a client becomes even more difficult when the client and the server communicate over a wireless link or network. A wireless platform (e.g., a wireless tablet) may be communicatively coupled to a server via a base station which acts as an bridge between a wired communication link to the server and a wireless communication link to the wireless platform. For example, a base station may encode an analog video input signal from the server to a MPEG (encoding scheme defined by the Moving Picture Experts Group) stream and send the MPEG stream to the wireless platform using IEEE 802.11b (2.4 GHz) wireless technology. The wireless platform receives and decodes the MPEG stream and displays the information. However, the amount of display information from the server to the wireless platform is an obstacle in implementing remote control of a server via a wireless client.
Generally, computer video graphics baseband data is large in size and requires a very fast transmission rate. For example, the picture size of a display monitor may be one thousand twenty-four (1024) by seven hundred sixty-eight (768) pixels. Thus a single frame is 18,874,368 Megabits (Mbits) in size or 18.9 Mbits/frame (1024 rows×768 columns×8 bits×3 colors). At a display refresh rate of 30 frames per second, this amounts to five hundred sixty seven (567) Mbits/second (Mbps) (18.9 Mbits/frame × 30 frames/second). Such data rate is too fast for most existing common data networks. The transmission rate for typical data networks is typically in the range of five (5) to twenty (20) Mbits/second.
Video compression permits a reduction in the size of data being transmitted. The Moving Picture Experts Group defined one widely used video compression scheme commonly known as MPEG. However, MPEG employs lossy compression and is optimized for natural motion pictures. Its performance is not good for computer graphics or text data. Computer graphics and text data typically include many sharp edges and flat plains. MPEG discards high frequency coefficients of Discrete Cosine Transform (DCT) to compress the data. As a result, a ghost edge or mosquito noise often appears around the edge of a previously compressed graphic or text.
FIG. 1A is an example of an original high-contrast edge. After the data is encoded and decoded, the edge has artifacts shown in FIG. 1B.
Another problem with MPEG is its compression ratio. It is usually twenty to one (20-1) to forty to one (40-1). This is not sufficient for transmitting computer graphics over a conventional network and permitting a client to control a server and viewing the server's display. That is, the network transmission rate together with video compression are insufficient to permit displaying the desktop of a remote server on the client's display at the original refresh rate. If the refresh rate on the server display is faster than the network through-put rate then the client's display has a noticeable delay and would hinder practical implementation of a remote controlled server.